Classical epidemiological studies on families, twins and adoptions have revealed a strong genetic influence in the development of suicidal behaviours. Clinical studies have also proved that a family history of attempted or completed suicide is associated with suicidal behaviours in all psychiatric diagnoses. Besides, the same rates of inheritance tell us that genetic factors are not the only determinants of suicidal behaviours, which have a multifactor basis. Influence of environment is likely to partly account for the variance in the expression of the suicidal phenotype, and has been implied in the stress-diathesis model of suicidal behaviours. Starting from the influential work by Asberg, et al. (1976), followed by the mounting evidence of a blunted serotonergic function in the suicidal brain, serotonergic genes have been the main focus of studies on the biology of suicide. In this general perspective, the Serotonin Transporter (SerT) gene has been intensively and extensively studied, namely in the latest 5 years, when investigations have grown in complexity by examining the genetic variation and its interaction with environment. In the following paper, results from the main studies investigating the gene-environment interaction of 5-HTTLPR in the psychiatric disorders associated with suicidal behaviours will be reviewed and discussed.